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<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
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<body>
    <script>

        var flag = true;
        console.log(!flag);

        //以下6个取反都为true
        console.log(!null);
        console.log(!undefined);
        console.log(!0);
        console.log(!"");
        console.log(!NaN);
        console.log(!false);

        console.log(!54);
        console.log(!"iwen");
        console.log(!{name:"iwen"});
        
        //&& 多个条件都要满足，任何一个不满足都为false
        console.log(100>10 && 100>20 && 100>30);

        // ||多个条件，满足一个则为真，都不满足才是false
        console.log(100 > 10 || 100  > 200);
    </script>
</body>
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